1. Field
The following description relates to signal processing and transmission technologies, and more particularly, to a Faster-Than-Nyquist (FTN) signal processing and transmission technologies.
2. Description of Related Art
In general signal transmission schemes, a pulse shape and speed are determined such that a signal can be transmitted within a given bandwidth, with no inter-symbol interference. Such pulse shaping is referred to as a Nyquist pulse shaping, which has a maximum transfer rate in a given bandwidth with no inter-symbol interference.
In order to increase a transfer rate of a transmission system that employs the Nyquist pulse shaping method, a signal is transmitted by narrowing a time interval of pulse shaping, or a symbol modulation level is increased. However, narrowing of the time interval of pulse shaping requires wider bandwidth, while increasing of symbol modulation level requires a higher signal-to-noise ratio to achieve the same amount of signal detection. For these reasons, research on an FTN transmission technology that can increase a transfer rate within the same bandwidth, without using a higher modulation level, has been conducted.
The FTN transmission technology is a method to transmit a signal by reducing a pulse period while preserving a form of pulse shaping that is limited by a bandwidth. This method causes inter-symbol interference (ISI) to necessarily occur in a transmission signal, but can achieve a higher transmission speed in the same bandwidth, as compared to the conventional Nyquist shaping method. If a signal is transmitted with the preserved pulse shape and at shorter intervals than a transmission interval at which the signal can be transmitted without ISI, inter-symbol overlap occurs, which leads to interference occurring. In this case, if a receiving apparatus has prior knowledge about a pattern of interference caused by said overlap, it is possible to generate a reference signal by creating artificial interference in the original signal and reconstruct a signal from which interference is removed by comparing the received signal with the reference signal.
In most radio communication systems, a receiver uses a pilot signal for initial system synchronization and carrier phase synchronization. The pilot signal does not carry actual data, but is used for coherent detection for which a transmitter and a receiver transmits and receives a designated signal. In a system to which an FTN transmission technology is applied, a pilot signal is distorted due to ISI.